The present invention relates to a water treatment method and a water treatment apparatus, for example, to a water treatment method and a water treatment apparatus for use in semiconductor factories and liquid crystal factories.
Treatment water contains organofluoric compounds as an example of compounds which are to be treated for water treatment. Organofluoric compounds are chemically stable substances. In particular, the organofluoric compounds have excellent properties from the viewpoints of heat resistance and chemical resistance, and therefore have been used for surface active agents or the like.
However, the organofluoric compounds, because they are chemically stable, are less easily microbially decomposable. For example, perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) as such organofluoric compounds are less decomposed in ecosystems. This incurs a fear for bad influences on ecosystems.
Specifically, it is said that perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are so chemically stable as to need high temperatures of about 1000° C. or more for their complete thermal decomposition. Also, PFOS and PFOA have hitherto been quite difficult to decompose with conventional treatments using microorganisms, photocatalysts or the like.
As a prior art, a method and an apparatus using nanobubbles are disclosed in JP 2004-121962 A.
This prior art utilizes the properties of nanobubbles such as decreases in buoyancy, increases in surface area, increases in surface activity, generation of local high pressure, surface activation or bactericidal action due to implementation of electrostatic polarization. In more detail, the prior art has disclosed that inter-association of those properties allows various objects in polluted water to be cleaned with high function and low environmental load by virtue of its polluting-component adsorbing function, high-speed cleaning function for object surfaces and bactericidal action, thus being enabled to achieve purification of polluted water.
As another prior art, a generation method of nanobubbles is described in JP 2003-334548 A.
In this prior art, it is disclosed that the method includes the steps of, in a liquid: (1) decomposing part of the liquid into gas; (2) applying ultrasonic waves in the liquid; or (3) decomposing part of the liquid into gas and applying ultrasonic waves.
As another prior at, a waste fluid treatment apparatus using ozone microbubbles is described in JP 2004-321959 A.
In this prior art, ozone gas generated from an ozone generator as well as waste fluid drawn out from a lower portion of the treatment tank are fed to a microbubble generation device via a booster pump. In this prior art also, generated ozone microbubbles are fed into the waste fluid within the treatment tank through an opening of a gas blowout pipe.
However, organofluoric compounds cannot be effectively microbially decomposed by the foregoing prior art.